During the rut (also known as the rutting period, and in sheep sometimes as tupping), males often rub their antlers or horns on trees or shrubs, fight with each other, wallow in mud or dust, and herd estrus females together.

The rut in many species is triggered by a shortening of the length of daylight hours each day. The timing of the rut for different species depends on the length of their gestation period (length of pregnancy), usually occurring so the young are born in the spring, shortly after new green growth has appeared (which provides food for the females, allowing them to provide milk for the young), and when the temperatures are warm enough that the young will not die of hypothermia.

The rut for white-tailed deer (Odocoileus virginianus) usually lasts from 1–3 months in the Northern Hemisphere and may occur most of the year in tropical zones. The rut is the time when white-tailed deer, especially bucks, are more active and less cautious than usual. This makes them easier to hunt, as well as more susceptible to being hit by motor vehicles.[1]

Some people believe that the white-tailed deer rut is also controlled by the lunar phase and that the rut peaks seven days after the second full moon (the rutting moon) after the autumnal equinox on 21 September. However, study of white-tailed doe conception dates conducted in Minnesota between 1980 and 1987 showed no correlation between peak breeding dates of white-tailed deer and any lunar phase.[2]

A white-tail doe may be in estrus for up to 72 hours, and may come into estrus up to seven times if she does not mate. Cow elk may come into estrus up to four or more times if they do not mate.